Rapid Microwave-Assisted Phloroglucinolysis in the Determination of Oligomeric Procyanidin Average Size in Fiber Extracts of Two Cocos nucifera L. Varieties

The coconut tree (Cocos nucifera L., Arecaceae) is a palm tree distributed in coastal vegetation across the tropics. Its fibers are the main agro-industrial residue from coconut production. Extracts obtained from the fibers contain procyanidins with biological and pharmacological potentials. The main analytical methods used to characterize procyanidins are based on the depolymerization reaction by acid catalysis in the presence of nucleophile in excess. This study aimed to optimize a modified depolymerization reaction using microwave irradiation and to apply this method to characterize the procyanidins from the fiber extracts of two coconut varieties. Fibers of C. nucifera var. typica A and var. typica were extracted with acetone:water 6:4 (v/v). After acetone was evaporated, the extracts were lyophilized and and then partitioned partitioned with ethyl acetate:water (1:1, v/v). The resulting aqueous fractions, rich in polymeric procyanidins, were analyzed by HPLC, in triplicate, after depolymerization. A factorial design was applied in duplicate, using irradiation power (50 to 350 W) and reaction time (10 to 50 s) as independent variables, and the product yield as the dependent variable. The optimized independent parameters were 200 W of irradiation power and 30 s of reaction time, reducing the reaction time by ca. 40 times when compared with the standard protocol. The aqueous fractions exhibited a mean degree of polymerization of 7.06 and 9.98, instead of 4.49 and 4.87 using microwave-assisted phloroglucinolysis compared to the conventional protocol. Epicatechin was the only extender unit found for both varieties and catechin was the preferred terminal unit (78.51% and 51.55%) as terminal unit. A significant increase in the mean degree of polymerization was found, indicating higher efficacy in the depolymerization of procyanidins. The coconut fibers are a potential source of procyanidins with a high degree of polymerization, making this agro-industrial waste suitable for industrial applications.